52 C. M. CHILD. 



According to Moszkovvski ('07, p. 420), the decreasing rapid- 

 ity of regulation with increasing distance from the oral end of the 

 body is due in Actinia cFgnina merely to the fact that below a 

 certain level a new cesophagus is formed and the parts of the old 

 oesophagus which remain hinder closure until they are cast off 



In Ceriantlius this is not the case. In all of the observed 

 cases any portion of the oesophagus which remains takes part in 

 the process of regulation and is not cast off. Moreover, differ- 

 ences in the rapidity of regulation are distinguishable both at 

 different levels within the oesophageal region and at different 

 levels aboral to it. It is to be expected that any difference 

 in capacity which might exist at different levels of the body 

 would be more marked in the greatly elongated body of Cerian- 

 tlms than in such a form as Actinia, where the body is relatively 

 short. At any rate, there is no doubt that such a difference 

 exists in very considerable degree in Ceriantlius. 



The most important results of my experiments with C. czstuarii 

 are stated in the following summary. 



1. \n C. CEstnarii, as in C. ^olitarius, the distension by water in 

 the enteric cavity is an essential factor in form -regulation. In its 

 partial or total absence the formation of disc and tentacles is re- 

 tarded or inhibited. 



2. The internal pressure is essential not only for the formation 

 of new parts, but for the persistence of the old. Partial or total 

 atrophy of the tentacles follows decrease or absence of distension 

 and the atrophied structures develop anew when distension is again 

 permitted to occur. 



3. The body-wall of C. cestuarii is much thinner and more deli- 

 cate than that of C. solitarius and is also much more sensitive to 

 changes in internal pressure. In the absence of distension even 

 the body-wall undergoes rapid atrophy and disintegration. 



4. In nature the walls of the burrow in which the animal lives 

 aid the body-wall in supporting the pressure resulting from dis- 

 tension, especially in the aboral region. If the animals are kept 

 in water without sand in which to burrow, the internal pressure 

 never reaches its normal amount. Under these conditions the 

 tentacles are more or less relaxed and undergo partial atrophy 

 and the aboral region of the body becomes greatly deformed and 



